Dstn display with electromagnetic shielding

ABSTRACT

The invention relates to a DSTN display with electromagnetic protection, comprising an active cell ( 1 ) and a passive cell ( 2 ), whereby the active cell ( 1 ) comprises electrodes ( 12, 13 ) and the passive cell ( 2 ) faces an observer of the display. The passive cell ( 2 ) comprises a metallic transparent layer ( 18, 19 ). Said metallic layer ( 18, 19 ) is electrically connected to a ground potential (G).

The invention relates to a DSTN display with electromagnetic shielding.The active cells have two transparent plates (for example made of glassor plastic) arranged at a distance from one another. Transparentelectrodes are fitted on the surfaces of the sides of the plates thatare assigned to one another, a liquid crystal substance being arrangedbetween said electrodes. Depending on the applied voltage, the liquidcrystal substance changes the plane of polarization of the lightpenetrating through the liquid crystal substance. Outside the liquidcrystal, a total of two pole filters are arranged in the beam path ofthe light penetrating through the liquid crystal cell, which filterstransmit light only in one plane of polarization. Thus, the light beamsare transmitted or blocked depending on the position of the pole filterswith respect to one another and the driving of the electrodes, with theresult that a correspondingly driven pixel of the display appears darkor bright.

The improvement of the image quality, in the case of DSTN cells, apassive cell is additionally arranged in the beam path of the light, inthe case of which passive cell a liquid crystal substance is likewisearranged between two transparent plates and has an opposite modularorientation in contrast to the liquid crystal substance of the activecell.

The driving of the individual pixels gives rise to electromagneticinterference on account of the high driving frequencies that occur inthis case, which electromagnetic interference can penetrate toward theoutside unimpeded if no countermeasures are implemented. Furthermore, inparticular in the context of use in motor vehicles, in the case of auser of the motor vehicle, due to friction between the user's clothingand cover materials of the motor vehicle seats or the seat belts of themotor vehicle, the user may be charged to high static voltages. If apart of the user's body then comes in proximity to the display, voltageflashovers may occur which may damage or even destroy the display.Therefore, it is known from the prior art to provide a metal frame forprotecting the display, but said metal frame means an additionalcomponent and is complicated and expensive to produce. Therefore, it isan object of the invention to specify effective electromagneticprotection which, moreover, is constructed inexpensively and simply.

According to the invention, the object is achieved by virtue of the factthat at least one of the bodies of the passive cell is provided with atransparent, electrically conductive layer that is connected to adefined potential, in particular the ground potential.

Thus, electromagnetic interference caused by the display is effectivelyshielded toward the outside. At the same time, the display is protectedfrom external interference.

A coating made of ITO (Indium Tin Oxide) has good transparency and isnot conspicuous.

The fact that the electrically conductive layer completely covers theplate in the display region means that a reliable shielding effect ispresent and the coating of the plate is particularly simple. Theconnection of the metallic layer to the ground potential can be realizedparticularly simply by means of a flexible sheet conductor.

Particularly good reliable shielding can be realized by virtue of thefact that the display, with the exception of the display regionperceptible by an observer, is surrounded by a housing made of metal ormetallized material.

The invention is explained in more detail below with reference to thefigures, in which:

FIG. 1 shows a section through a DSTN display according to theinvention;

FIG. 2 shows a partial section P from FIG. 1;

FIG. 3 shows a section through an embodiment with a metallic housing.

A display A has an active cell 1 and a passive cell 2, the passive cell2 facing a possible observer B. the display A is surrounded by acovering 3. The active cell 1 is electrically conductively connected viaa connection 4 to a control circuit 6—which is arranged on a printedcircuit board 5—via a control line 6 a. The passive cell 2 iselectrically conductively connected to a ground potential G via aflexible sheet conductor 7. An optical waveguide 29 serves for backlighting of the display.

FIG. 2 reveals the construction of the DSTN display. The active cell 1has two transparent plates 10, 11 on which electrodes 12, 13 arerespectively arranged. A liquid crystal substance 14 is situated betweenthe electrodes 12, 13. The passive cell 2 likewise has two transparentplates 15, 16 covered, preferably areally, on their inner sidesrespectively by a transparent, electrically conductive layer 18, 19,preferably ITO (indium tin oxide). A liquid crystal substance 20 issituated between the electrically conductive layers 18, 19. A polefilter (20, 21) is respectively applied areally on the outer sides ofthe plates 10, 16, so that initially unpolarized light can penetrateinto the active cell in polarized fashion. If no voltage is present, asin the case of the liquid crystals 14 a, 14 b illustrated, the plane ofpolarization of the light is rotated through approximately 270°. If avoltage is present, as is illustrated on the right for the liquidcrystals 14 c, 14 d, the plane of polarization of the light is notrotated in the active cell. Liquid crystals 20 a-20 d of the passivecell do not lie in a voltage field and all rotate the plane ofpolarization of the light through 270° in a direction of rotationopposite to the direction of rotation of the liquid crystals 14-14 d ina non-driven state. Color effects are thus compensated for. If theelectrodes 10, 12 are driven, the polarized light can penetrate throughthe pole filter 22, as is illustrated by the arrow a.

FIG. 3 reveals that the display A, with the exception of the regionvisible to the observer B, is surrounded by a housing 30 made of metalor metallized material. The housing 30 is electrically conductivelyconnected to the electrically conductive layers 18, 19 illustrated inFIG. 2.

The invention can readily be modified. Thus, it suffices, by way ofexample, to provide only one of the two electrically conductive layers18, 19. Furthermore, it suffices if the electrically conductive layer isnot applied completely areally, but rather is partly interrupted undercertain circumstances.

1-4. (canceled)
 5. A Double Super Twisted Nematic display withelectromagnetic protection, comprising: an active cell havingelectrodes; a passive cell, wherein said passive cell is arranged at afront of said display and faces an observer of the display, said passivecell having an electrically conductive transparent layer electricallyconnected to a predetermined potentional, said electrically conductivelayer being at least partly interrupted such that it.
 6. The display ofclaim 5, wherein said electrically conductive transparent layer consistsessentially of indium tin oxide.
 7. The display of claim 5, furthercomprising a flexible sheet conducts connecting said electricallyconductive transparent layer to said predetermined potential.
 8. Thedisplay of claim 5, further comprising a metallic housing surrounding arear and sides of said display, said electrically conductive transparentlayer being electrically connected to said housing.
 9. The display ofclaim 5, wherein said predetermined potential is ground potential.